1. Field of the Invention
The present general inventive concept relates to a light scanning unit assembly including a plurality of light scanning units, and more particularly, to a light scanning unit assembly having a skew adjuster to adjust a skew of a plurality of scanning lines produced by the plurality of light scanning units such that the plurality of scanning lines are skewed at an equal angle with respect to a horizontal line, an electrophotographic image forming apparatus including the light scanning unit assembly, and a method of adjusting a scanning line skew.
2. Description of the Related Art
In general, an electrophotographic image forming apparatus scans a beam on a photosensitive medium charged to a predetermined potential to form an electrostatic latent image on an outer circumference thereof, develops the electrostatic latent image as a visual image with a toner that is a developing agent, and transfers and fixes the toner image onto a sheet of paper for printing. Printing a color image using electrophotography typically requires a plurality of developers containing developing agents of different colors. However, depending on the printing method used, the color printing may require one or a plurality of photosensitive media or light scanning units for scanning a beam onto the photosensitive medium.
FIG. 1 is a diagram illustrating a scanning line skew in an electrophotographic image forming apparatus for producing a color image. Referring to FIG. 1, the electrophotographic image forming apparatus includes four photosensitive media 10, 20, 30, and 40 and four light scanning units (not shown) corresponding to the four photosensitive media 10, 20, 30, and 40, respectively. Each of the four light scanning units scan a beam onto the corresponding photosensitive medium 10, 20, 30, or 40 according to an image signal.
Due to dimension errors or assembling tolerances required for mounting the light scanning units on a frame (not shown), scanning lines 11, 21, 31, and 41 produced by the four light scanning units, respectively, are slightly slanted away from a horizontal line extending along the longitudinal direction of the corresponding photosensitive medium 10, 20, 30, or 40. This slight slant away from the horizontal line is referred to as “scanning line skew.”
While a skew between each of the scanning lines 11, 21, 31, and 41 and a horizontal line of the corresponding photosensitive medium 10, 20, 30, or 40 falls within a predetermined tolerance, a skew between the respective scanning lines 11, 21, 31, and 41 may fall outside the predetermined tolerance. The presence of skew between the plurality of respective scanning lines 11, 21, 31, and 41 falling outside the predetermined tolerance may cause discrepancies in color superposition at a boundary between images, thus significantly degrading quality of a printed image.
FIG. 2 is a schematic front view illustrating a conventional light scanning unit assembly including a skew adjuster designed in an attempt to overcome the problem described above. Referring to FIG. 2, the conventional light scanning unit assembly includes four light scanning units 50, 60, 70, and 80 arranged in a column-like arrangement and a frame that supports the four light scanning units 50, 60, 70, and 80. Ends of each of the four light scanning units 50, 60, 70, and 80 are propped up by a pair of supports 91 and 92 of the frame 90. As the skew adjuster, the light scanning unit assembly further includes a sloping member 95 interposed between an end of each of the light scanning units 50, 60, 70, and 80 and the support 92. By adjusting a distance between each of the light scanning units 50, 60, 70, and 80 and the respective sloping member 95, the slope of each of the light scanning units 50, 60, 70, and 80 can be adjusted.
However, the conventional light scanning unit has a drawback in that it is difficult to finely adjust the distance between each of the light scanning units 50, 60, 70, and 80 and the respective sloping member 95. Adding another element for fine skew adjustment may complicate the structure of the skew adjuster. Another drawback is that it is difficult to achieve a compact size due to a large width between both sides of the frame 90.